"I'm sure that what he's produced will be examined by the relevant authorities. I do note that Mr Slipper asserts that these are fabrications. I'm not a handwriting expert. The authorities will sort this matter out once and for all," he said.

The Coalition is also continuing to insist that Mr Slipper does not return to the Speaker's job while he faces separate claims that he sexually harassed a staff member.

Opposition Leader Tony Abbott said this morning that if Mr Slipper was in the Speaker's chair when Parliament resumes for the budget, it would be a sign that Prime Minister Julia Gillard did not take sexual harassment seriously.

Shadow treasurer Joe Hockey echoed the sentiment, saying the "commonsense view" was that Mr Slipper should stand down from the "most significant position in the Parliament" until he is cleared of all claims against him.

"I'm a member of Parliament, I have standards, this is not up to my standards," Mr Hockey told Channel 7.

Ms Gillard is still standing by Mr Slipper's plan to return to the Speaker's chair if he is cleared of the specific allegations that he had rorted his Cabcharge entitlements.

Mr Slipper is expected to face a motion of no confidence in the Parliament if he does try to return to his job for the budget sittings. Independents Rob Oakeshott, Tony Windsor and Andrew Wilkie have all indicated they would consider voting with the Coalition to prevent Mr Slipper's return.

But Mr Abbott and Mr Wilkie said this morning that they did not expect Mr Slipper to be in the chair on May 8.

The Opposition Leader told Channel 9 this morning that his "strong instinct", given "unhappiness" in the Labor caucus about Mr Slipper, was that it was unlikely the embattled Speaker would try and return to the Speakership in May.

"Lets wait and see what he does," Mr Abbott said. "I would be very surprised if [Ms Gillard] tries to force the issue in the Parliament."

Mr Wilkie said he did not think it would come down to a vote against Mr Slipper, but added that if the Queensland MP did try and return while still under the cloud of sexual harassment allegations, there would likely be move against him.

"I would not be surprised if there is a motion of no confidence if he's in the chair," Mr Wilkie told ABC Radio National this morning from Hobart.

Mr Wilkie also said that he would be prepared to move the motion, arguing that the Speaker "safeguards the standards of the Parliament".

But Greens Leader Christine Milne was not prepared to say whether the Greens MP Adam Bandt would support such a motion in the lower house. Senator Milne said it was right that Mr Slipper had stood aside at the weekend, but stressed that he was entitled to the presumption of innocence. "Trial by media is unhelfpul to the national debate and the Parliament," she told Radio National.

Mr Slipper is yet to respond in detail to the allegations that he sexually harassed his adviser, James Ashby, 33, earlier this year.

Yesterday, the Member for Fisher said that he will make a further statement in "due course".

"I repeat that I reject allegations that have been made against me," he said.